Naphthalene diazoquinone

Positive photoresists, by contrast, are based on water-soluble novolak resins with naphthalene diazoquinone sulfonate (NDS) as the photosensi-tiser. On photolysis the NDS causes a rearrangement in the polymer to yield nitrogen gas plus an indene carboxylic acid. This latter functional group considerably increases the solubility of the polymer, hence solubilising those areas of the polymer that had been exposed to light. 

The addition of specialized small molecules to a polymer coating is the functional basis for most photoresists. Conventional positive-working photoresists function owing to the difference in solubility caused by the imagewise exposure of a small molecule naphthalene diazoquinone sulfonate ester (NDS). The presence of this small molecule dramatically inhibits the dissolution of the novolac binder while its photodecomposition accelerates the binder dissolution in aqueous base. 

The resist system that we have explored is based upon the photochemistry of naphthalene diazoquinone in a base-soluble polymer matrix. This type of system is of interest because it is the basis for all commercial near-UV photoresists. The photochemistry is old but recently has been studied in detail (1). Reaction scheme 1 shows the series of reactions and rearrangements that occur after the photolysis of a dicizoquinone in the presence of water. 

There are three major events in the reaction sequence. First the naphthalene diazoquinone is destroyed. Second, nitrogen gas is released. Third, an acid is produced. 

A review of synthetic methods for the most popular photoactive compounds used in diazoquinone resists—DNQ-5-sulfonate and DNQ-4-sulfonate—has been provided by Ershov et al. The synthesis typically begins with naphthalene derivatives, and proceeds via introduction of a sulfonic acid group, followed by diazotization and reaction with thionyl chloride to yield the sulfonic acid chloride (Scheme 7.2). In the next step, the chloride is reacted in a base-catalyzed esterification with a suitable ballast group or backbone, which usually is a multifunctional phenol, less frequently a monofunctional phenol or an aliphatic alcohol. ... 

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